Hey all! Kind of a basic question that I feel a little sheepish asking, but I'm very new to the live plant world.

In my 8 gallon Fluval Flora with 3 wpg lighting, I have tried to keep several plants. None have done really all that well except the crinum, despite my efforts to help them out with Fluorin Multi, CO2, etc. Then today I checked my nitrates etc. as part of my weekly routine and found this:
Ammonia: 0 ppm
Nitrite: 0 ppm
Nitrate: 0 ppm

My last water change was last week, about 10-15%. I dosed some Nutrafin Plant Gro which contains a little nitrogen... but basically I think my plants aren't growing due to a lack of nitrogen. Am I correct in assuming so? I have a reasonable bioload from fish in there and am feeding every day or every other day, so I think my plants might consuming nitrates quicker than nitrates can be produced.

My main question is... do I stop doing water changes while frequently checking nitrates until I get them up to around 10-20 ppm? Or should I keep on with the water changes and find some way to supplement nitrogen?

Many years ago when fighting BGA the advice given here was to get some Nitrates in by way of Potassium Nitrate, aka KNO3, aka Saltpeter (at your local pharmacy). IIRC the prescription was 1/4 teaspoon for every 20Gal (just scale that down) after each 20-25% water change. Monitor levels of course, etc.